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1.8 KiB

; cache disable routine
public DisableCache
code segment ; simple but effective for demonstration purposes
;* DisableCache() *
;* *
;* This routine disables cache(s) on a 486 or Pentium processor *
;* *
;* NOTE: due to the protection schemes incorporated into the 486 and *
;* Pentium processors, it will NOT work in virtual 8086 mode. *
;* *
;* written on Thursday, 2 November 1995 by Ed Beroset *
;* and released to the public domain by the author *
CR0_CD equ 040000000h ; Cache Disable bit of CR0
CR0_NW equ 020000000h ; Not Write-through bit of CR0
DisableCache proc
pushf ; save the flags
push eax ; save eax
cli ; disable interrupts while we do this
mov eax,cr0 ; read CR0
or eax,CR0_CD ; set CD but not NW bit of CR0
mov cr0,eax ; cache is now disabled
wbinvd ; flush and invalidate cache
; the cache is effectively disabled at this point, but memory
; consistency will be maintained. To completely disable cache,
; the following two lines may used as well:
or eax,CR0_NW ; now set the NW bit
mov cr0,eax ; turn off the cache entirely
pop eax ; restore eax
popf ; restore the flags
ret ; return to caller
DisableCache endp
code ends